1. Field of the Invention
The present invention relates to a flexure provided with wiring and used for a head suspension of a hard disk drive. In particular, the present invention relates to a flexure having wiring, capable of solving the problems of electrostatic discharge and ion migration that are trade-offs. The present invention also relates to a method of manufacturing such a flexure and a head suspension employing such a flexure.
2. Description of Related Art
A hard disk drive (HDD) has a head suspension to support a head for writing and reading data to and from a hard disk. The head suspension includes a flexure. The flexure has a substrate made of a resilient stainless steel thin plate, a base insulating layer made of flexible resin formed on the substrate, wiring patterns formed on the base insulating layer and connected to terminals of a magnetic head, and a cover insulating layer made of flexible resin formed over the wiring patterns.
The flexure is assembled into a head suspension by, for example, clamping. During the assembling work, the surface of the cover insulating layer of the flexure may be rubbed to have positive or negative electrostatic charge. The electrostatic charge causes an electrostatic induction phenomenon to electrostatically charge the wiring patterns of the flexure. In addition, a slider on which a magnetic head is arranged may also be electrostatically charged. When attaching the slider to the head suspension, the wiring patterns of the flexure must be connected to terminals of the magnetic head. At this moment of connection, the electrostatic charge of the wiring patterns and slider is released at once, to deteriorate or destroy a read element of the magnetic head.
Recent hard disk drives employ sensitive magnetic heads such as MR heads and GMR heads, or more sensitive ones such as TuMR heads. These magnetic heads are vulnerable to disturbances such as electrostatic discharge (ESD), and therefore, there is a strong requirement for a measure to cope with ESD.
The present applicant has proposed in United States Patent Application Publication No. US2006/0187587A1 a technique of coping with an electrostatic discharge failure of a magnetic head. This technique forms a conductive flexible resin coating on the surface of a flexure over a read wiring pattern. Also, the present applicant has disclosed in United States Patent Application Publication No. US2006/0190673A1 a technique of forming a cover insulating layer on a flexure from slightly conductive flexible resin, the cover insulating layer and a base insulating layer sandwiching wiring patterns of the flexure. These related arts can prevent the deterioration and breakage of a read element caused by electrostatic discharge.
The inventors of the present invention have found through studies that the quality and reliability of a flexure are influenced not only by electrostatic discharge of the flexure but also by wire-to-wire or wire-to-substrate ion migration of the flexure. The ion migration is a phenomenon that ions move along a nonmetallic medium between wiring patterns or between wiring patterns and a metal substrate of the flexure. The ion migration and electrostatic discharge are trade-offs and are very difficult to simultaneously solve them. What is craved is an innovative technique capable of solving both the problems of ion migration and electrostatic discharge.